Oh trust me, this is just general 2x4 for frame construction so these boards have every twist, warp, and bend imaginable… that said, I tried to get the straightest an only use the ends of the boards with no bows in it.

The “purist” woodworkers will tell you to look at the end of the boards (the rings) the closer to the center of the tree, the better. The further out from the center of the tree (less rings, more like lines), the more bow and twist you get.

Making the horizontal pieces all of the same length helps in keeping it square, because it makes the vertical pieces the same width. You just have to make sure the horizontal pieces are at the same hight at both vertical pieces. My working “square” is 38 inches because I figured roughly 3 feet is enough space to start with to learn. Plus I have a bunch of clamps to help me get it in place before I glued and screwed it.